This invention relates to an acceleration detector for detecting the acceleration and deceleration of a moving body such as an automobile.
Among known acceleration detectors, there is a type having a magnetic body mounted so as to move when subjected to acceleration and a differential transformer for detecting its movement.
One example of this type is shown in FIG. 8. With this differential transformer type acceleration detector 71, when it is subjected to acceleration in the direction of arrow A in the figure, a magnetic body 74 supported by leaf springs 73a and 73b moves in the direction of arrow B in the figure while resiliently deforming the leaf springs. With this movement, the portion of the magnetic body 74 located inside a secondary coil 77b at the righthand side of the figure becomes longer than its portion located inside a secondary coil 77a at the lefthand side, thus producing a difference in induced voltage between the secondary coils 77a and 77b. The acceleration is detected by this difference.
In the figure, numeral 78 designates a primary coil, and 72 a case. One prior art example of this type is disclosed in Japanese Unexamined Utility Model Publication 59-95266.
With this type of detector, if the acceleration is small, the magnetic body moves little, producing too small a voltage difference to be detected clearly. Thus, its detection sensitivity is poor.
With the known detector, the leaf springs for suspending the magnetic body might suffer a permanent deformation or might be destroyed if an excessive acceleration acts on magnetic body 74.
Further, because a difference in voltage is produced by the relative movement between the secondary coil and the magnetic body, they have to be positioned with high accuracy. This will lower the assembling efficiency, take a long time and thus increase the assembling cost.